Field of the Invention
The invention relates to an apparatus for the microprogram control of information transfer, and to a method for operating the same.
An integrated high-performance DMA control ADMA (advanced direct memory access), may have four mutually independent channels which accomplish the data transfer between media (memories, peripheral equipment) or, more generally, between data sources and data sinks. The main control of the channels is taken over by microprograms which are stored within the electronic module in a microcommand memory ROM.
The microprograms are divided into two main groups: Organization programs which read the necessary control information from the command blocks deposited in the organization memory upon starting the channel or in concatenating or linking commands or data and redepositing control information, such as status information, in the organization memory after a data transfer, and also perform internal administration, so that the organization programs (ORG programs) control the control transfer; and
DMA programs which carry out the data transfer proper. The organization programs are formed of ORG microcommands. The control transfer controlled by ORG microcommands is comparatively simple and is controlled exclusively by ORG microcommands themselves. This takes about 80 microcommands. Contrary to the control transfer by ORG programs, DMA transfer is substantially more complex due to the large number of parameters to be taken into consideration, such as physical and logical bus widths of the data source and the data sink, direction of counting, manner of counting of the pointer addresses, even or odd pointer addresses, address straightening (ALIGN) for reducing the bus transfers, and so on. If all of these DMA cases were controlled purely by microprogram-type control transfer, several hundred microcommands would be required for all of the DMA cases. This takes space in the microcommand memory ROM and accordingly reading time as well.
It is accordingly an object of the invention to provide an apparatus for the microprogram control of information transfer and a method for operating the same, which overcomes the hereinaforementioned disadvantages of the heretofore-known apparatus and methods of this general type, which requires little space in the microcommand memory ROM and short reading times, and which permits a high transfer rate and a short reaction time to transfer requests.